1. Field of the Invention
The present invention relates to an apparatus for separating a luminance signal and a chrominance signal, and more particularly, to an apparatus for separating a luminance signal and a chrominance signal from an NTSC composite video signal.
2. Description of the Related Art
In contemporary color television systems, a chrominance signal is superimposed on a luminance signal to provide a composite video signal. Meanwhile, an image system, such a monitor, outputs a composite Red(R)/Green(G)/Blue(B) signal. The composite RGB signal is generated from the luminance and chrominance signals. For this reason, color television receivers require a circuit adapted to separate the composite video signal into the luminance signal and the chrominance signal.
Owing to recent advances in digital techniques, conventional analog luminance/chrominance signal separating apparatus have developed into digital luminance/chrominance signal separating apparatus for separating the luminance and chrominance signals. The conventional analog luminance/chrominance signal separating apparatuses separate the composite video signal in a horizontal direction whereas the digital luminance/chrominance signal separating apparatuses separate the composite video signal in a vertical direction by the using line memories.
FIGS. 1 and 2 are block diagrams of conventional luminance/chrominance signal separating apparatuses. Referring to FIG. 1, a first conventional luminance/chrominance signal separating apparatus 101 includes a line memory 111, a low-pass filer 121, and subtractors 131 and 132. The line memory 111 delays a digital composite video signal VS1 by 1 horizontal period. The subtractor 131 subtracts the digital composite video signal VS1 from a signal S1, which is delayed by 1 horizontal period. The low-pass filter 121 filters a subtracted signal P1 and then outputs a chrominance signal C1. The subtractor 132 subtracts the chrominance signal C1 from the signal S1, which is delayed by 1 horizontal period, and then outputs a luminance signal Y1.
Referring to FIG. 2, a second conventional luminance/chrominance signal separating apparatus 201 includes line memories 211 and 212, subtractors 231, 232, and 233, an adder 241, and a low-pass filter 221. The line memory 211 delays a digital composite video signal VS1 by 1 horizontal period. The line memory 212 further delays a signal S1, which has already been delayed by 1 horizontal period, by 1 horizontal period. Thus, the line memory 212 outputs a signal S2 that is delayed by 2 horizontal periods. The subtractor 231 subtracts the digital composite video signal VS1 from the signal S1, which is delayed by 1 horizontal period. The subtractor 232 subtracts a signal S2, which is delayed by 1 horizontal period, from the signal S1, which is delayed by 2 horizontal periods. The adder 241 adds signals P1 and P2 output from the subtractors 231 and 232. The low-pass filter 221 filters a signal P3 output from the adder 241 to output a chrominance signal C1. The subtractor 233 subtracts the chrominance signal C1 from the signal S1, which is delayed by 1 horizontal period, to output a luminance signal Y1.
The luminance signal Y1 and the chrominance signal C1 exist in the same frequency band of the frequency spectrum. Thus, the luminance signal Y1 output from the apparatus shown in FIGS. 1 and 2 contains chrominance signal components, which is referred to as “cross-luminance”. The chrominance signal C1 contains luminance signal components, which is referred to as “cross-chrominance”. Cross-luminance and cross-chrominance degrade resolution in the vertical direction.